A hard disk drive (HDD) used as an information-storage device includes a magnetic-recording head including a read element and a write element. A write element of the magnetic-recording head writes data to, or alternatively, erases data from, data bits arranged on a circular track of a magnetic-recording disk, which includes an information-storage medium. The read element reads a magnetic signal recorded by the write element. The magnetic-recording head is disposed in a head-slider body forming the head-slider. The head-slider is mounted on a suspension arm. The suspension arm applies a compressive force to the head-slider in a direction of the magnetic-recording disk. When the magnetic-recording disk is rotated, the head-slider flies on a film of air formed on the recording surface of the magnetic-recording disk caused by rotation of the magnetic-recording disk.
The surface of the magnetic-recording disk includes a protective layer, which is covered with a lubricating film, for preventing the magnetic-recording head from getting worn and corroded. In order to reduce the spacing between the magnetic-recording head and the magnetic recording layer, also referred to herein by the term of art, “fly height,” for increasing magnetic recording area density, the lubricating film is decreased in thickness of a monomolecular layer. The monomolecular layer of lubricant is kept at the interface between the head-slider and the magnetic-recording disk in order to maintain the reliability at the interface between the head-slider and the magnetic-recording disk. Mobility is an intrinsic property of the lubricant; the lubricant is sufficiently immobile so as not to be easily displaced by slider-disk contact, but is mobile enough so that any lubricant lost from the lubricant residing in the lubricating film can be easily replenished.
The head-slider includes an air-bearing surface (ABS) facing the magnetic-recording disk. While the magnetic-recording disk is being rotated, the magnetic-recording disk drags air under the head-slider along the ABS in a direction approximately parallel to the tangential velocity of the magnetic-recording disk. As the air passes beneath the ABS, the air is compressed to increase the pressure between the disk surface and the ABS of the head-slider, which creates a hydrodynamic lifting force, which is referred to by the term of art, “lift,” that counteracts the compressive force to lift the head-slider, allowing the head-slider to fly in proximity with the recording surface of the magnetic-recording disk.
Once the HDD is operated, four kinds of forces: hydrodynamic force, Van der Waals' force, electrostatic force, and air shearing stress may cause the lubricating film to move. Among the four kinds of forces, the air shearing stress is the dominant one for the movement of the lubricant. Since the air shearing stress moves the lubricant to the underside of the head-slider, droplets of the lubricant are formed on the surface of the head-slider that faces the magnetic-recording disk.
For a head-slider having an extremely low fly height, an extremely strong relationship exists between the motion of the lubricant droplets and the airflow on the underside of the head-slider. Most of the lubricant droplets are moved to the trailing edge of the head-slider by the air shearing stress. These forces and the effects of these forces on lubricant mobility and distribution are of interest to engineers and scientists engaged in HDD manufacturing and development who seek to meet the rising demands of the marketplace for increased data-storage capacity, performance, and reliability.